I won't use pro-line foams at all any more and that has lead me to buy GRP tires as well. I used pro-lines with holes, without holes, it does not matter. The foam seems to be made for the pros who will only run them a few heats & then put on new ones.
I love that statement above telling us to put hole in everything to let out the moisture that has already destoryed the foam. Take a pole, how many off-road racers never run on a wet track or need to wash tires. Maybe some guys who are lucky enough to have a clay indoor track but that's about it.